Prime Minister Neville Chamberlain and the War Cabinet approved the plan, and Churchill began assembling the mines. The French government and military, however, remained cool to the idea, especially Premier Édouard Daladier. By March 1940, Britain had assembled more than 6,000 mines, and Churchill wanted to begin deploying them in the Rhine.
The Allied Supreme War Council then endorsed plans to lay mines along the Norwegian coast and bomb the Ruhr in combination with Operation royal marine in an effort to shut down German industry. However, newly appointed French Premier Paul Reynaud, fearing German retaliation with a possible strike on Paris, rejected royal marine and any bombing or mining of German industry, so only the mining of the Norwegian coast went forward in April. Reynaud insisted on a three-month delay before launching royal marine in order to give the French air force time to prepare for German retaliation. He later agreed that Britain could launch the operation should German forces invade France or Belgium.
Royal Marines hastily implemented the plan after German troops opened their offensive into France on 10 May 1940. In the first week of fighting, they placed more than 1,700 mines into the Rhine. These effectively halted river traffic between Karlsruhe and Mainz and damaged several pontoon bridges. By 24 May, British Marines had placed more than 2,300 mines, and these drifted into the Rhine, Moselle, and Meuse Rivers. In the closing days of the campaign, the Royal Air Force dropped some additional mines in night sorties. As Churchill later wrote, Operation royal marine's limited success was "swept away in the general collapse of French resistance." The operation did, however, lay the groundwork for later minelaying efforts by both the RAF Bomber Command and the RAF Coastal Command. Over the next two years, the British placed almost 16,000 mines, which sank some 369 German vessels for an estimated total of 361,821 tons.
Stephen K. Stein
Ashley, L. R. N. "The Royal Air Force and Sea Mining in World War II." Air University Quarterly Review 14, no. 4 (Summer 1963): 38–48.; Churchill, Winston S. The Second World War. Vol. 1, The Gathering Storm. Boston: Houghton Mifflin, 1948.; Ellis, Lionel F. The War in France and Flanders, 1939–1940. London: Her Majesty's Stationery Office, 1953.; Gilbert, Martin, ed. The Churchill War Papers. Vol. 1, At the Admiralty, September 1939–May 1940. New York: Norton, 1993.